The present invention relates to a grease composition for constant velocity joints used in motorcars, in particular, for plunging type constant velocity joints. A very high surface pressure is applied to the constant velocity joint to be lubricated and abnormal vibrations may often be caused due to complicated rolling and sliding motions of the joint. Accordingly, the present invention, more specifically, relates to a grease composition for constant velocity joints which can effectively lubricate such constant velocity joints to thus efficiently reduce frictional force and to efficiently inhibit the occurrence of any vibration thereof.
Examples of lubricating greases conventionally used in such constant velocity joints include a grease comprising a calcium complex soap as a thickening agent; and a grease comprising a lithium soap, as a thickening agent, and a sulfur-phosphorus atom containing extreme pressure agent selected from the group consisting of, for instance, sulfurized fats and oils and, tricresyl phosphate and zinc dialkyldithiophosphate.
In the recent motorcar industries, the number of FF-type motorcars have rapidly increased from the viewpoint of making the weight thereof lighter and of securing the dwelling space and the constant velocity joints (CVJ) indispensable to the achievement of such purpose have widely been used therein. Among the CVJ's, the plunging type constant velocity joints, in particular, tripod type constant velocity joints (TJ), double offset type constant velocity joints (DOJ) and the like cause complicated rolling and sliding motions at a certain angle and hence generate slide resistance in the axial direction during the rotational motion thereof and this becomes a cause of vibrations during idling, rolling of a car body during starting and speeding up thereof and emission of beating sounds and/or sounds filled within the car observed at a specific velocity. Various methods for improving the structures of the constant velocity joints (CVJ) per se have been proposed in order to solve this problem, but the improvement thereof is difficult from the viewpoint of the space occupied by the joint, and the weight and cost thereof.